Bending/shaping or stirrup-making machines are known, hereafter shaping machines. The bending units or devices of such machines are fed with oblong metal products such as metal wire from a roll, or precut bars, to make reinforcement stirrups for the building trade. Hereafter these base materials, whether they come from a roll or are already in bars, will be referred to generically as metal wire.
It is also known that, upstream of the bending unit, shaping machines include drawing and straightening means to feed the metal wire to the operating units of the machine, such as shears and at least one bending unit.
The difficulties encountered in the drawing and straightening step of the metal wire arriving from rolling are known, which difficulties increase when the metal wire is fed to the shaping machine from a roll. In the metal wire arriving from rolling there are tensions that remain dormant until a simple bend or other is induced. This problem increases in the case of metal wire arriving from a roll, since the wire should be extracted from a reel that may or may not rotate around its own axis in order to facilitate the unwinding of the wire.
Furthermore, in the case of metal wires intended to make stirrups for reinforcements for concrete, metal alloys have appeared that confer on the metal wire physical and/or chemical properties that it did not have before, properties that accentuate the working difficulties.
These problems are more evident in the case of metal wires for reinforcement rods.
Due to the surface ribs present, such metal wires have discontinuous surfaces and a shape that is not always perfect.
It is therefore obvious that a simple bending operation made on the metal wire is conditioned by the tensions present therein, so that the possible geometric forms made with the metal wire not only do not keep the desired geometric disposition, but do not even maintain the flat spatial disposition.
In the case of reinforcement stirrups therefore, unwanted shapes are obtained with different angles and/or with the sides spatially three-dimensional.
The stirrups are therefore unusable, or are poor quality and low reliability when installed, and generally speaking should be discarded. In addition, in the case of metal wire for reinforcement rods, given the continuous variation in its section, the correct and accurate drawing and/or straightening becomes uncertain, not constant and not uniform.
It must be said here that metal wires for reinforcements have an extensive range of measurements, which can go from 5 mm to 24 mm and more in diameter, and that a shaping machine must be able to work all this range of sizes always and in any case obtaining a perfect product.
It goes without saying that the problems raised by a metal wire with a diameter of 5 mm are therefore much less than those raised by a metal wire with a diameter of 24 mm, at least in terms of size.
It must also be noted that in a shaping machine the drawing and straightening means take on another considerable importance, since they also have the function of defining the measurements required on each occasion between one bending operation and the next.
When the drawing and straightening means do not perform their function constantly and without errors, it is not possible either to make stirrups or other shapes of metal wire with the desired sizes, or to make a plurality of identical stirrups, whether in sequence or not.
It is understood that the drawing and straightening means should be configured both to feed a single metal wire, and also two or more metal wires fed in parallel and simultaneously.
Purpose of the present invention is to obtain a drawing and straightening apparatus that can operate continuously and precisely with any type of metal wire whatsoever, in particular metal wire for reinforcements. This serves to guarantee that the advance of the metal wire is constant, uniform and the correct value on each occasion, also preventing rotations of the metal wire upon itself during advance. To this purpose a total requalification of the way to approach the drawing and straightening apparatus has been made.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.